The invention relates to a disc brake for a commercial vehicle.
Monitoring of the wear of the brake pads and/or the brake disc takes place, above all, for reasons of operational safety of a disc brake, with the result that a required replacement of the respective brake pad takes place at a best possible time. Here, the wear state of the brake pads is to be determined as accurately as possible in advance.
The replacement of the brake pads is required at an optimum time, in particular, for economic reasons. It is to be aimed for here that a replacement is carried out only when the respective friction pad has been used down to a permissible minimal thickness. A premature replacement would be contrary to the optimization of the operating costs in this regard, whereas a replacement which is too late would entail an impairment of the functional safety of the disc brake overall.
Various structural solutions are known for detecting the wear state of the brake pads. For instance, a wear indicator is used, in which a current-conducting cable is guided through the pad carrier plate, which cable is severed in the case of wear of the friction pad and generates a signal in a signal generator, usually in the driver's cab of the motor vehicle.
Furthermore, wear indicators are known which, by means of a rotary potentiometer, determine a movement travel of an adjusting device which results in the case of an adjustment of the brake pads in order to compensate for a wear stroke, which movement travel can likewise be seen, for example by the driver of the vehicle, by way of a display device.
For example, a device which has a spring-loaded pin which is guided in the brake caliper and by way of which a wear-induced adjustment of the brake caliper can be seen is used for visually detecting the wear state of the brake pads, in accordance with the characterizing type.
However, the realization of a wear indicator of this type is associated with considerable structural complexity, just like the realization of the remaining known wear indicators. For example, complicated machining of the brake caliper is required in order to guide the pin.
The electric wear indicators can likewise be implemented only with considerable apparatus complexity and, moreover, cannot ensure absolutely reliable functioning, on account of the severe operating conditions in which commercial vehicles are frequently used.
DE 36 12 166 C2 proposes providing the brake carrier with a marking for visual detection of the wear state of the brake pads and/or the brake disc, which marking serves for wear detection in correspondence with a correspondingly modified pad carrier plate.
Here, the brake carrier-side markings are produced by way of a corresponding shape, in particular by way of U-shaped or V-shaped recesses in the sense of notches.
However, recesses of this type, and also other necessary shapes, have an influence on the strength of the brake carrier, the notches, above all, leading to a reduction in the fatigue fracture strength.
A common feature of all devices for wear detection is that they can be seen substantially only when the vehicle wheel is removed, which prevents an optimized use of the device.
The invention is based on the object of developing a disc brake of the generic type in such a way that a simple, reliable and accurate wear indicator of the brake pad is possible with low structural and manufacturing complexity.
This object is achieved by way of a disc brake having a brake caliper which engages over a brake disc, is held on a stationary brake carrier such that it can be displaced axially in relation to the brake disc, and in which brake pads are positioned which can be pressed against the brake disc by way of a brake application device during a braking operation. The brake caliper is mounted for axial displacement on at least one guide bar which is connected to the brake carrier. A device for visual wear detection of brake disc and/or brake pad wear is provided, wherein, for wear detection, a comparison element which runs parallel to the guide bar, extends in the opposite direction to the brake disc and has at least one step is fastened to the brake carrier.
A comparison element which is fastened according to the invention to the brake carrier, extends parallel to the guide bar of the brake carrier, is oriented in the opposite direction to the brake disc, and has a step, is particularly simple and inexpensive to manufacture and to assemble. This results in a significant cost reduction, in comparison with the abovementioned wear contacts or continuous wear sensing by way of the above-described potentiometer.
All deformations of the comparison element, such as notched portions, stamped recesses, grooves, notches or the like, are to be considered to be a step in the broadest sense.
The arrangement of the comparison element so as to run in the opposite direction to the brake disc permits wear detection without it being necessary for the vehicle wheel to be removed.
The visual recognizability of the wear state is assisted by way of the step which, in correspondence with an edge of the brake caliper, makes it possible to detect that the minimum permissible thickness of the friction pad has been reached, said edge and the step being aligned visually.
In order to establish a visual distinction here, that is to say in order for it to be possible to detect the wear state even in the case of unfavorable light conditions, the step, just like the edge of the brake caliper, can be marked in color.
Since the comparison element is provided as a separate component, a change of the brake carrier and/or other components of the disc brake is no longer required.
According to one advantageous development of the invention, the comparison element consists of an angled-away metal sheet which is clamped in between the guide bar and the brake carrier, to which end an eyelet is integrally formed on the comparison element, which eyelet is penetrated by the shank of a screw, by way of which the guide bar is fastened to the brake carrier.
According to another variant of the invention, the comparison element is arranged between a ring of a folding bellows and the brake carrier, the ring of the folding bellows being supported on the eyelet. The folding bellows serves to protect the guide bar in the region which lies exposed between the brake caliper and the brake carrier.
According to a further concept of the invention, the comparison element is configured as a pin which is pressed into an eye of the brake carrier and is held in a frictionally locking manner therein.
The comparison element is extremely simple to manufacture in every form, whether as a sheet metal strip or as a pin, as a turned part (pin) or as a bar/formed part (sheet metal strip). In contrast to electric wear detection, as described with respect to the prior art with a contact conductor which is embedded in the friction pad, the novel wear detection means does not cause any abrasion during operation, with the result that the invention also affords corresponding advantages for environmental protection reasons.
In addition to the particularly inexpensive manufacturing capability, the in principle universal applicability is to be emphasized. In particular, retrofitting of a disc brake which has already been assembled is possible without a problem, the comparison element being configured in such a way that it can be mounted on the brake carrier both on one side and on the other side in the connector region of the brake caliper. In this case, two guide bars are provided, of which one is a constituent part of a locating bearing and the other is a constituent part of a floating bearing. The possibility of clamping the comparison element between the guide bar or between the folding bellows and the pad carrier may be suitable here.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.